A turbine, particularly a steam turbine, generally has a large number of valves that can be used as fresh steam valves, interception valves or diversion valves. The opening position of each of the valves serves the purpose of regulating a respective material charge or steam charge and can be generally regulated with the help of a transmission member, in particular a part of a valve actuator, allocated to the respective valve. The requirements on the valve in terms of specifications have to be particularly high with respect to regulating power and regulating speed.
To ensure a secure operation or closure of the valve, in particular in an emergency shutdown of a steam turbine, valves can be configured as oil-hydraulic driven servo valves, whereby the actuators allocated to them in each case include an oil-hydraulic unit either with a central hydraulic supply system or a de-centralised hydraulic supply system as described in European Patent Application EP 0 040 732 A1. Due to improvements in electrical motors with respect to reliability and momentum also a servo valve for regulating of pressure and/or quantity of charging medium can be used as for example described in German Patent Application DE-OS 19 37 198 relating to atomic plants, chemical plants and similar plants. The servo valve described therein has a push rod on which a valve seat is fixed. The push rod is coupled with an electrical servo motor over a beam rotatable around a central fulcrum. In this way the quantity of charging medium can be regulated through the valve. A return spring grips on to the push rods.
In EP 0 230 849 A1, a servo valve and a stop valve are described. The servo valve has a locking body that can be shifted along an axis, which also has a piston stretching along the axis. The piston is configured as a straightgeared rack that stays in contact with the longitudinal gearing of another rod. By rotating the rod round its rod axis, one can achieve shifting of the locking body in a axial direction. Rotation of the rod takes place with the help of another toothing at the end of the rod via an electrical motor.
In DE 44 46 605A1, a valve for a steam turbine is described which has a valve spindle with a sealing seat disposed against it. The valve spindle is driven by an electrical motor that is connected to the valve spindle through an electromagnetically activated coupling. For an automatic servo-closing of the valve, this includes a plate spring system.
In International publication WO 98/13633 A1, an actuator for a turbine valve whose opening position can be adjusted by way of the connecting rod, such that interference-free operation of the valve is ensured with a particularly low fire-risk is described. The actuator includes an electrical motor for driving the connection rod. The connecting rod is connected to the electrical motor via a rack and pinion system and via an electromagnetic tooth coupling.
International publication WO 99/49250 A1 describes an electromechanical actuator for a valve, in particular a steam turbine. The actuator has a connecting rod and an electrical motor for driving the connecting rod. The connecting rod is connected to the electrical motor through a transmission device producing a torque, which can vary according to axial displacement of the connecting rod. The connecting rod is connected to a crank disk which itself is connected via a tooth coupling with the electrical motor.